Dell Latitude 3160 does not have keyboard backlight, but there is a
sysfs interface for it, which does nothing at all.
KBD_LED_ON_TOKEN is the only token can be found. Since it doesn't have
KBD_LED_OFF_TOKEN or KBD_LED_AUTO_*_TOKEN, it should be safe to assume
at least two tokens should be present to support keyboard backlight.
Not all models have ON token - they may have multiple AUTO tokens instead.
Models which do not use SMBIOS token to control keyboard backlight, also
have this issue. Brightness level is 0 on these models. Verified on Dell
Inspiron 3565.
Reports keyboard backlight is supported only when at least two modes are
present.